1. Field of the invention
The present invention relates to an abnormal combustion detection apparatus and an abnormal combustion detection method for detecting abnormal combustion caused by pressure vibration in a combustion chamber of an internal combustion engine.
2. Description of the Related Art
Knock control systems have become normal equipment in recent automotive gasoline engines. A typical knock control system includes a knock sensor provided in a cylinder block for detecting an engine knock on the basis of pressure vibrations that occur in a combustion chamber at a frequency band specific to engine knocking. If the knock sensor detects an engine knock, the combustion chamber temperature is decreased by delaying the igniting timing so as to prevent extension or growth of the knocking. Therefore, the ignition timing is maintained at or near the minimum spark advance for the best torque while the engine knocking is substantially prevented or minimized, so that high output can be achieved.
In a recent technology for improving the fuel consumption efficiency and reducing emissions, the compression ratio setting is increased and the air-fuel ratio is set to a stoichiometric value. This technology tends to increase the combustion temperature, and gives rise to a danger of causing preignition, that is, spontaneous ignition that occurs earlier than the set ignition timing, if an engine knocking occurs and adds to the increase in combustion temperature. To cope with this problem, Japanese Utility Model Application Laid-open No. HEI 1-88042 proposes an abnormal combustion detection method that performs a knock determination based on a pressure pulsation that is detected in a combustion chamber by a knock sensor when preignition occurs. If the knock sensor detects the pressure pulsation during a predetermined period of time prior to the set ignition timing, it is determined that preignition has occurred. If the knock sensor detects the pressure pulsation after the set ignition timing, it is determined that engine knocking has occurred.
Japanese Patent Application Laid-open No. HEI 9-236073 proposes a technology wherein an ion current that occurs at the time of preignition is extracted to an ignition coil.
However, the abnormal combustion detection method based on detection of a pressure vibration, as disclosed in Japanese Utility Model Application Laid-open No. HEI 1-88042, is unable to discriminate until after the ignition timing a pressure pulsation caused by an engine knocking resulting from preignition that occurs immediately before the ignition timing from a pressure pulsation caused by an engine knocking that occurs after the ignition timing. Therefore, the method has a problem of a considerable delay in determining occurrence of preignition. The technology as disclosed in Japanese Patent Application Laid-open No. HEI 9-236073 needs a device for detecting an ion current, thereby requiring a complicated system construction and suffering a disadvantage in cost. Thus, there is a strong demand for quick detection of preignition through the use of a signal from a conventional knock sensor.